Off road or heavy truck tires are often subjected to rough road conditions that produce repetitive, localized high pressure pounding on the tire. These stresses can cause fatigue fracture and can lead to crack formation and growth. This degradation of the tire has also been referred to as chipping or chunking of the tread surface or base material.
In an attempt to prevent this degradation, it is known to add reinforcements such as carbon black, silicas, silica/silanes or short fibers to tire compositions. Silica has been found advantageous because of its ability to deflect and suppress cut prolongation, and silanes have been added to bind the silica to unsaturated elastomers. The fibers that have been added include nylon and aramid fibers.
It is also known that the addition of polyolefins to rubber compositions can provide several beneficial properties. For example, low molecular weight, high density polyethylene, and high molecular weight, low density polyethylene, are known to improve the tear strength of polybutadiene or natural rubber vulcanizates. In the tire art, it has also been found that polyethylene increases the green tear strength of carcass compounds and permits easy extrusion in calendering without scorch. Polypropylene likewise increases the green strength of butyl rubber. Polypropylene, has also been effective in raising the static and dynamic modulus of rubber, as well as the tear strength of the rubber.
Although the addition of polyolefins to rubber compositions is known to provide several beneficial effects, the addition of polyolefin to tire recipes has, heretofore, had a deleterious affect on the mechanical, wear, and hysteresis properties of tires, as well as handling and ride comfortability of the tires.
Accordingly, there remains a need in the art to improve the tear strength of rubber vulcanizates, especially those deriving from tire compositions, without sacrificing the other properties of vulcanizates, tire components, or tires.